Problem: Solve for $k$ : $k - 9 = 3$
Explanation: Add $9$ to both sides: $ \begin{eqnarray} \\ k - 9 &=& 3 \\ \\ {+9} && {+9} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{-9 + k} &\hphantom{=}& \hphantom{3} \\ k &=& 3 {+ 9} \\ \end{eqnarray} $ Simplify. $ k = 12$